Vern,
Im going under the assumption that each of the firewalls currently installed are Cisco PIX firewalls. If they are PIX firewalls its pretty simple to implement a 3DES secure VPN from each site to each other. Before you start there are going to be a bunch of question that you need to supply your self with answers first before you start.
At least my initial question were:
I recommend reading up on IPSEC first. There is nothing worst that trying to implement something without knowing all or your options; such as do I use pre-share or a PKI infrastructure.
Cisco VPN Introduction:
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/vpn.htm
How do I manage this?
Ive been playing with the Cisco secure policy manager, and so far I like it.
Try this link, they also have a 30 day eval.
http://www.cisco.com/warp/public/cc/pd/sqsw/sqppmn/
How do I configure this?
Follow this link, more that enough information here to get you in trouble. The examples have really good example scenarios and explanations.
http://www.cisco.com/warp/public/700/configsec.html
Which products should I use?
You all ready have the firewalls, the only thing you have to do is provide a management platform.